Try saving/favoriting the following searches. That way, you will be automatically notified by email when the items comes up on eBay. I do this all the time and I am able to find holy grails within a month.

-Kenny pillow-Kenny large plush-Kenny giant plush-Kenny Rare

If you don't mind daily notifications, you can always favorite 'kenny plush' on searches.

Be sure to watch southparkdude356's items on eBay as well. I got a lot of South Park holy grails from him. He is the one who sold the Kenny pillow plush you wanted not too long ago. It was up on eBay for a while so if you have the money ready next time, you should be able to snag it with little to no competition.